Abstract: A digital telephony session instantiation and control system comprises a plurality of mobile terminals in operable communication with a server executing a session controller across an IP network. Each mobile terminal is associated with a profile and the session controller is configured for matching non-disassociated user profiles and signalling to instantiate a digital telephony session between associated mobile. The session controller is configured to terminate the session upon expiry of a timer unless receiving first in-call input signals from both mobile terminals, terminates the session responsive to a second in-call input signal received from either mobile terminal and terminates the session and disassociates the profiles responsive to a third in-call input signal received from either mobile terminal.

Abstract: Antiparasitic milbemycin derivatives having at the C.25 position a substituted 2-propenyl group --C(CH.sub.3).dbd.CH--R.sup.2 wherein R.sup.2 is a C.sub.3 -C.sub.8 alkyl, alkenyl or alkynyl group which may optionally contain an oxygen or sulphur atom as part of the chain, or a C.sub.3 -C.sub.8 cycloalkyl or cycloalkenyl group, or a 3 to 6 membered oxygen or sulphur containing heterocyclic ring which may optionally be substituted by one or more alkyl groups or halogen atoms; and process for their preparation.